The present invention is directed to coated receiver sheets, such as papers and transparencies. More specifically, the present invention is directed to coated receiver sheets suitable for use with aqueous-based inks such as those employed in ink jet printing. In one embodiment, the receiver sheet is a paper which comprises a substrate having a Hercules sizing degree of at least about 50 seconds and a basis weight of less than about 90 grams per square meter, and a coating which comprises a pigment and a binder comprising polyvinyl alcohol and an additional binder component selected from the group consisting of styrene-butadiene latices, cationic polyamines, cationic polyacrylamides, cationic polyethyleneimines, styrene-vinyl pyrrolidone copolymers, styrene-maleic anhydride copolymers, polyvinyl pyrrolidone, vinyl pyrrolidone-vinyl acetate copolymers, and mixtures thereof. In another embodiment, the receiver sheet is a transparency comprising a substantially transparent substrate and a coating which comprises a pigment and a binder comprising polyvinyl alcohol and an additional binder component selected from the group consisting of styrene-butadiene latices, cationic polyamines, cationic polyacrylamides, cationic polyethylenelmines, styrene-vinyl pyrrolidone copolymers, styrene-maleic anhydride copolymers, polyvinyl pyrrolidone, vinyl pyrrolidone-vinyl acetate copolymers, and mixtures thereof. Receiver sheets according to the present invention exhibit particular advantages when employed in ink jet printing processes in that they exhibit uniform solid area colors, reduced bi-directional color banding in mixed primary colors, waterfastness, reduced inter-color mixing with neighboring colors, high optical density, improved coating adhesion to the substrate with less chalking, and, in the case of papers, a more plain paper-like feel.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The second type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink-filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again.
Ink jet printers of the continuous stream type employ printheads having one or more orifices or nozzles from which continuous streams of ink droplets are emitted and directed toward a recording medium. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. Printing information is transferred to the droplets of each stream by electrodes that charge the passing droplets, which permits each droplet to be individually charged so that it may be positioned at a distinct location on the recording medium or sent to the gutter for recirculation. As the droplets proceed in flight from the charging electrodes toward the recording medium, they are passed through an electric field which deflects each individually charged droplet in accordance with its charge magnitude to specific pixel locations on the recording medium. The continuous stream ink jet printing process is described, for example, in U.S. Pat. No. 4,255,754, U.S. Pat. No. 4,698,123, and U.S. Pat. No. 4,751,517, the disclosures of each of which are totally incorporated herein by reference.
Papers coated with materials compatible with ink jet inks are known. For example, U.S. Pat. No. 4,478,910 (Oshima et al.) discloses an ink jet recording paper comprising a base sheet with a Stockigt sizing degree of less than 4 sec. (based on a basis-weight of 60 g/m.sup.2) and a coating layer comprising a water-soluble polymeric binder and fine silica particles having a specific surface area of more than 200 m.sup.2 /g as measured by the BET method and a uniformity number n of the Rosin-Rammler distribution of greater than 1.10. The polymeric binder may include polyvinyl alcohol or its derivatives, water soluble cellulose derivatives, water soluble polymeric substances such as polyvinyl pyrrolidone, or the like.
U.S. Pat. No. 4,758,461 (Akiya et al.) discloses a recording paper suitable for ink-jet printing comprising a fibrous substrate paper on the surface of which a silicon containing type pigment and a fibrous material of the substrate paper are present in a mixed state, said recording paper having a Stocklgt sizing degree of from 0 to 15 sec. and a basis weight of from 90 to 200 g/m.sup.2. The paper can also contain an aqueous binder such as one or a mixture of two or more water-soluble or water-dispersed polymers such as polyvinyl alcohol, starch, oxidized starch, cationized starch, casein, carboxymethyl cellulose, gelatin, hydroxyethyl cellulose, SBR latex, MBR latex, vinyl acetate emulsion, and the like.
U.S. Pat. No. 4,780,356 (Otouma et al.) discloses a recording sheet suitable for ink jet printing comprising a sheet of paper and porous particles on the paper surface, wherein the particles have an average pore size of from 10 to 5,000 Angstroms, a pore volume of from 0.05 to 3.0 cc/g and an average particle size of from 0.1 to 50 microns. The particles can be coated on a paper surface by means of a binder such as polyvinyl alcohol.
U.S. Pat. No. 4,474,847 (Schroder et al.) discloses a coated base paper for use in ink jet recording process wherein the coating comprises a pigment and/or filler of non-flake structure and a binding agent dried on the paper. The pigment content is at least about 90 percent by weight of the dried coating and has a particle mean diameter of about 0.05 to 4.0 microns, and the binding agent is predominantly hydrophilic.
U.S. Pat. No. 4,554,181 (Cousin et al.) discloses an ink jet recording sheet having a recording surface which includes a combination of a water soluble polyvalent metal salt and a cationic polymer, said polymer having cationic groups which are available in the recording surface for insolubilizing an anionic dye.
U.S. Pat. No. 4,304,815 (Cugasi, Jr.) discloses an aqueous release coating composition for application to substrates, wherein the coating has low absorption to the substrate, excellent adhesion to the substrate, and easy and quick release and removal from the substrate. The coating comprises from about 3 to about 8 percent polyvinyl alcohol, from about 9 to about 35 percent clay, from about 5 to about 12 percent of an adhesive binder, and from about 49 to about 75 percent water. The clay can be any of variously colored natural mixtures of silica and alumina as well as occasional amounts of oxides of magnesium, calcium, and potassium having a particle size range of from about 1/4 micron to about 4 microns. The adhesive binder can be substantially any commercially available synthetic thermoplastic homopolymer, copolymer or terpolymer having the necessary adhesive properties, chemical stability, and the like, such as polyvinyl acetate homopolymers and copolymers, polyvinyl chloride-polyvinyl acetate copolymers, polyvinyl acetate-acrylic copolymers, and the like.
U.S. Pat. No. 4,617,239 (Maruyama et al.) discloses a method of coating paper to improve its surface strength and printability by applying to the paper a silicon-containing modified polyvinyl alcohol agent or its saponification product. The coating agent forms a film on the surface of the paper which minimizes the penetration of the coating into the paper and improves the surface strength and printability of the paper. The coating agent may be incorporated with other coating compounds, including synthetic resin emulsions such as styrene-butadiene latex, polyacrylate ester emulsion, polyvinyl acetate emulsion, vinyl acetate-acrylate ester copolymer emulsion, and vinyl acetate-ethylene copolymer emulsion. Further, the coating agent may be incorporated with pigments such as clay, calcium carbonate, titanium dioxide, satin white, zinc oxide, silica, aluminum oxide, and cadmium sulfide.
Copending application U.S. Ser. No. 07/616,971, entitled "Carbonless Paper for Ink Jet Printing," inventors John F. Oliver, Richard E. Sandborn, and David J. Sanders, filed Nov. 21, 1990), the disclosure of which is totally incorporated herein by reference, discloses a process for generating images which comprises (1) incorporating into an ink jet printing apparatus a carbonless paper set which comprises a first sheet comprising a support containing a color developer capable of reacting with a color former to produce a color image, said color developer comprising high surface area silica particles, and a second sheet comprising a support coated with the color former; (2) forming an image on the first sheet by causing ink to be expelled in droplets on a surface containing the color developer; and (3) forming an image on the second sheet by causing ink to be expelled in droplets onto the surface opposite to that coated with the color former.
Although known compositions are suitable for their intended purposes, a need remains for coated receiver sheets suitable for use with aqueous-based inks. In addition, there is a need for coated receiver sheets suitable for color ink jet printing processes. A need also exists for coated receiver sheets that enable uniform solid printed areas. Further, there is a need for coated receiver sheets that exhibit reduced bi-directional color banding in mixed primary colors. There is also a need for coated receiver sheets with high degree of waterfastness. A need also exists for coated receiver sheets with reduced inter-color mixing of neighboring colors. In addition, there is a need for coated receiver sheets that enable prints with improved optical density and color saturation. Further, there is a need for coated receiver sheets that exhibit improved coating adhesion with less chalking. There is also a need for coated papers with a texture that resembles that of plain paper to the touch.